1. FIELD OF THE INVENTION
This invention relates to the manufacture of stringers for slide fasteners wherein a train of fastening locking elements is attached to one edge of each tape of the stringers.
2. DESCRIPTION OF THE PRIOR ART
The prior art contains a number of methods and apparatus for manufacturing slide fastener stringers wherein a train of fastening elements is secured to an edge of a tape such as by stitching the fastening elements to the edge of the tape; by bonding the fastening elements to the edge of the tape with ultrasonic energy, adhesives and the like; or by weaving the train of fastening elements to the edge of the tape during the formation of the tape from tape forming members such as weft and warp threads. U.S. Pat. No. 3,054,364 illustrates an apparatus for stitching a train of fastening elements to the edge of a tape.
In the prior art, the count or number of fastening elements per unit length of tape made in a continuous manufacturing operation often varies so that sections of the stringer cannot be mated with certain other opposite stringer sections without exhibiting undesirable curvature of the slide fastener chain, i.e., when a stringer with one fastening element count per unit length is mated with an opposing stringer with a different count per unit length, the chain formed by the stringers will have a curvature. The ability of stringers to mate with opposing stringers without exhibiting any significant curvature or other incompatability is called "scramble" ability.
In many of the prior art stringer manufacturing operations, the assembly of the fastening element trains and the stringer-tape-forming members, such as tapes or warp threads, is made while such stringer-tape-forming members are under tension. Variation in the stress/strain relationship or the elasticity of the stringer-tape-forming members causing variation in the fastening element count per unit length when the stringer is relaxed after assembly is a major obstacle to the scrambleability of stringers.